In the prior art, electronic switches use LEDs to indicate by illumination the on and off of operating voltage to electrical equipment to indicate start and shut down functions of motors and electrical appliances. Both series and shunt regulators are used to control on/off operation of LEDs in the prior art.
Verkhovskiy, U.S. Pat. No. 6,075,448, teaches and claims a test value apparatus capable of differentiating between a shunt circuit and a low resistance value. A light emitting diode (LED) provides indications of the voltage values, the LED being so connected to enable variation of light by the LED in a manner inversely indicating resistance values across the circuit. The test apparatus comprises a shunting resistor for creating a shunt around the LED and a shunting switch for momentarily connecting the shunt so the LED provides an indication of the presence of a short in the circuit.
Jiang, U.S. Pat. No. 5,309,084 teaches and claims an electronic switch with on/off fading comprising a bridge rectifier and a thyrister. A triggering branch has a trigger pulse including a series connection branch of a voltage regulator diode and capacitor or LED. The nonlinear characteristics of the voltage regulator diode or LED inactivate a synchronic integrator circuit in an “on” stationary state, thereby reducing the forward bias of the diode in the trigger pulse integrator and reducing the angle of triggering. The triggering of the thyrister initiates the fading on process. As the trigger angle increases, the thyrister is cut off in the fading off process.
Nelson, U.S. Pat. No. 4,028,057 teaches and claims a plurality of light emitting diodes (LEDs) arranged to form an analog display in proportion to the gas present as read by a gas analyzer. Each LED is shunted by an electronic switch to ground having a control element whereby each LED is turned off when the catalytic and resistance elements of the gas analyzer warm up and generate an output which turns on an LED in the analog display. The electronic switch is in the form of an n-p-n transistor between the hot side of an additional LED and ground.
Marshall, U.S. Pat. No. 6,153,980, teaches and claims an LED array having plurality of LEDs connected in series with at least one active shunt connected in parallel across one or more of the LEDs and digital control logic for detecting an open circuit and activating active shunts to restore a closed circuit condition. Each of the active shunts is an active switching device, such as a power MOSFET or a bipolar transistor connected in parallel across each LED.
Lanzisera, U.S. Pat. No. 5,495,147, teaches and claims an LED light system comprising a plurality of LEDs connected in parallel and a regulated power supply providing a constant current and a constant voltage from an AC line input, a rectifier for rectifying the voltage, and a voltage regulator to provide a constant voltage and constant current wherein a zener diode limits the voltage fed into the voltage regulator.
Brown, U.S. Pat. No. 4,898,229, teaches and claims a low voltage thermostat for controlling operation of a heating and cooling system with a voltage regulator in series with an LED for detecting an over-voltage whereby an over-voltage causes the voltage regulator comprising a zener diode to break over and the LED to illuminate and indicate the over-voltage.
O'Malley, U.S. Pat. No. 4,647,831, discloses a rechargeable battery-operated appliance system wherein a switch provides a shunt around an LED which illuminates when the device is placed in a charging stand.
McBrian, U.S. Pat. No. 4,470,039 discloses an alarm shunt arrangement which provides an LED indicator light to indicate an alarm condition when the shunt switch is activated.
Engel, U.S. Pat. No. 4,027,227, discloses a combination series and shunt voltage regulating system which comprises a sensor for controlling a series regulator of transistors. The shunt regulator comprises a zener diode.
Accordingly, Verkhovskiy '448 discloses a shunting resistor and a shunting switch; Jiang '084, an electronic switch with on/off fading; Nelson '057, a plurality of LEDs and n-p-n transistor electronic switch; Marshall '980, a plurality of shunts in parallel across respective LEDs; Lanzisera '147, a zener diode and voltage regulator provide constant voltage and constant current; Brown '229, LED illumination when over-voltage causes a zener diode to break over; O'Malley '831, a shunt around an LED which illuminates during operation of a device; McBrian '039, an LED indicates an alarm condition when a shunt arrangement is activated; and Engel '227, a combination shunt and series voltage regulating system comprising a zener diode shunt regulator and a series regulator of transistors.
Accordingly, in the prior art it is well-known to utilize electronic switches with LED on/off fading, and shunt and switch regulators to turn LEDs on and off. However, a limited range low voltage testing and indicating device comprising a detector and low voltage regulator and measurer of magnitude in a switch-regulated power supply circuit wherein indicator LEDs operate to indicate separately the presence of voltage, a higher voltage, and an over-voltage has not been taught in the prior art.